Quiet hydraulic pump



Sept. 28, 1965 Filed June 19, 1963 A. LEHRER ETAL QUIET HYDRAULIC PUMP 3 Sheets-Sheet 1 FIJ.

INVENTOR. ALEXANDER LEHRER GUY L. JOHNSON Se t. 28, 1965 A. LEHRER ETAL 3,208,397

QUIET HYDRAULIC PUMP Filed June 19, 1963 3 Sheets-Sheet 2 INVENTOR. ALEXANDER LEHRER ATTYS.

p 1965 A. LEHRER ETAL 3,208,397

QUIET HYDRAULIC PUMP Filed June 19, 1963 3 Sheets-Sheet 3 I08 88 v I06 I04 M 02 0 INVENTOR.

ALEXANDER LEHRER United States Patent 3,208,397 QUIET HYDRAULIC PUMP Alexander Lehrer, Alexandria, and Guy L. Johnson,

Arlington, Va, assignors to the United States of America as represented by the Secretary of the Navy Filed June 19, 1963, Ser. No. 289,468 7 Claims. (Cl. 103-162) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to hydraulic power transmission systems, and more particularly it relates to reciprocatmg pumps.

It is desirable for reciprocating pumps to operate as quietly as possible, especially in ships, and submarines. However, much noise results from the sudden exposing of fluid at one pressure in a piston cylinder to inlet or discharge fluid at a different pressure during the operation of such reciprocating pumps.

Acoustic treatment, such as the use of flexible mountings, has not been entirely successful in many applications. Other methods such as the use of bleeder slots between the high and low pressure fluids or precompression by out-of-phase piston strokes vary greatly in effectiveness with the amount of pressure and the length of stroke of the piston. Bleeder slots in the port or valve plate which allow some leakage from the high to the low pressure volumes before each piston is completely opened to the piping system require a compromise in size between that needed for pressurizing and that required to limit leakage. The best design size varies greatly with pumping conditions. Changing the phase position of the valve plate with pressure to permit precompression by piston motion fails to account for changes in piston stroke. Consequently, designers have been forced to employ heavier, less flexible and more costly pumps, such as constant displacement pumps.

Accordingly, it is an object of this invention to provide an improved reciprocating pump.

It is a further object of this invention to provide a reciprocating pump having low noise characteristics.

It is a further object of this invention to provide a hydraulic pump having high efficiency, low cost of manufacture, and low operating noise.

It is a still further object of this invention to provide a reciprocating pump in which noise is reduced even though the stroke lengths of the pistons may vary.

It is a still further object of this invention to provide an improved valve plate for use in a low-noise reciprocat ing pump.

It is a still further object of this invention to provide a low-noise reciprocating pump in which fluid containing chambers pressurize or decompress the cylinders at the end of the piston travel so as to reduce the shock which normally occurs when a cylinder is brought into a different pressure than that in the cylinder.

It is still another object of this invention to provide an improved valve plate for a low-noise reciprocating pump, which valve plate contains all of the pressure chambers, auxiliary ports, valves, and passages, thus being easily adaptable to install on presently existing hydraulic machines in place of their present valve plates and thus allowing the cylinder ports to be substantially larger than would be possible if the auxiliary ports, valves and passages were located in the barrel.

It is still another object of this invention to provide a low-noise reciprocating pump which may pump or overhaul either from left to right or from right to left.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal cross-sectional view of part of an embodiment of the invention;

FIG. 2 is a transverse cross-sectional view taken on a plane indicated by the line 2-2 of FIG. 1;

FIG. 3 is a transverse cross-sectional view of a valve plate used in an embodiment of the invention;

FIG. 4 is a longitudinal cross-sectional view of the valve plate taken on a plane indicated by the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary cross-sectional view of the valve plate and the barrel assembly during a cylinder pressurizing stage in the operation of an embodiment of the invention; and

FIG. 6 is a partial transverse cross-sectional view of a reversing valve assembly which can be used in an embodiment of the invention.

Referring now in particular to FIG. 1, a longitudinal cross-sectional view of part of a positive-displacement variable-stroke parallel-piston hydraulic pump which is an embodiment of the invention is shown. This pump is similar to the pumps disclosed in the copending applications S.N. 206,104, filed June 28, 1962 and SN. 200,005, filed June 4, 1962.

A casing 10 of this pump is closed at one end by a head 12 and at the other end by an annular cover 14, which is attached to the casing 10 by the bolts 16. The head 12 is provided with an inlet passage 18 and an outlet passage 20, which passages are arranged to communicate with a valve means in the form of a stationary circular valve plate 22. A cylindrical shaft 24 is journaled in the anti-friction bearings 26 and extends through the valve plate 22 into the interior of the casing 10. A cylindrical barrel assembly 28 is fixedly mounted on the shaft 24 and adapted to rotate therewith. The barrel assembly is spaced from the interior of the casing 10 by means of roller bearings 30 which allow the barrel assembly to rotate within the casing.

The cylindrical barrel assembly 28 comprises a cylindrical barrel body 32 having a plurality of circumferentially spaced cylinders 34 formed therein, said cylinders being equally radially spaced from and extending parallel to their axis of rotation which is represented by the shaft 24, as can best be seen in FIG. 2. The cylinder ports or flow slots 36 are located adjacent to the valve plate 22 and are adapted to effect a communication, through the valve plate 22, with the inlet passage 18 and the outlet passage 20 at predetermined locations in the rotation of the barrel assembly 28 with respect to the valve plate 22.

A piston 42 having a ball head 44 is located within each cylinder and is adapted to reciprocate therein. Each ball head 44 is journalled in an associated shoe or slipper 46 which rides freely along the face of a swash plate 48 as the shaft 24 rotates the barrel assembly. The swash plate has a control shaft 50 which controls its angularity. Since the swash plate is disposed angularly or inclined to the axes of the cylinders and pistons, it actually forms a cam surface that causes the pistons 42 to reciprocate as they are being rotated by the barrel 32.

As was aforementioned, the inclination or angularity of the swash plate is controlled by the control shaft 50. When the plane of the swash plate is perpendicular to the axes of the pistons, which is vertical in the embodiment shown in FIG. 1, the stroke of the pistons is zero. As the swash plate is inclined, the stroke of the pistons is increased. At maximum inclination of the swash plate,

a forty-five degrees displaced from the vertical, the stroke of the pistons is at its maximum.

An insert 52 is mounted in the end of shaft 24 and locked to the barrel body 32, thereby locking the shaft and barrel body together so that they rotate as a unit. A plunger 54 is mounted in the insert 52 and extends to the center of the swash plate, with one end of the plunger being spaced away from the bottom of the insert by compression spring 56 and the other end of the plunger pressing against a spherical ball 58. The ball 58 freely seats in a seat on the swash plate 48 in such a manner that the spherical ball 58 acts as a bearing against which the swash plate bears, so that the swash place can be rotated through a range of positions on opposite sides of the shaft 24 as indicated by the arrow in FIG. 1. The swash plate can be moved to any position within degrees on either side of the vertical position, thereby allowing reversible or bi-directional flow. For example, FIG. 1

, shows the machine operating as a pump, with lower pressure fluid being introduced through inlet 18. As the cylinder assembly 28 is rotated by the shaft 24, the pistons compress the fluid and discharge it under high pressure when the associated cylinder communicates with the outlet 20.

The machine of FIG. 1 can also pump in the opposite direction as that recited above. That is, lower pressure fluid could be introduced through the outlet 20, and as the cylinder assembly is rotated by the shaft 24, the pistons would compress the fluid and discharge it under high pressure when the associated cylinder is in communication with the inlet 18. To accomplish this, the swash plate 48 would have to be moved by the control shaft to a position where it would be angularly displaced on the other side of the vertical position. An upwardly directed centerline for the control shaft 50 is shown in FIG. 1 at the upper arrow 59, which would correspond to the position of the control shaft under such reversed conditions.

If it were desired to use the machine only for unidirectional flow, that is only for pumping and overhauling in one direction the swash plate could be mounted to rotate about a line normal to an axis of one of the pistons, rather than normal to the axis of the centerline of the shaft. An arrangement such as this is shown in United States Patent No. 1,506, 892. Such an arrangement has the advantages of allowing greater variations in the length of stroke of the positions, and also of keeping to minimum the volume in each cylinder at zero stroke, thus keeping to a minimum the amount of energy that can cause noise; however, such operation is achieved through the sacrifice of the feature of reversible or bi-directional flow. The reversing flow can then be provided by a valve operated with the pump stroke control shown in FIG. 6.

Referring now to FIG. 3, a valve plate 22 is shown, which plate may be used in either the reversible or the non-reversible types of swash plate mountings described above. The valve plate is provided with a circular series of ports which are radially arranged to align with the cylinder slots 36. The cylinder slots 36 are narrower than the piston 42 and extend beyond the cylinder 34 outwardly from the center of the barrel assembly 28. The cylinder slots 36 are best seen in FIGS. 1 and 2.

The ports include two elongated main ports 68 and 62 and two auxiliary ports 64 and 66. A passage or bore 38 shown in FIG. 1 connects the main port with the inlet 18 and a passage or bore 40 also shown in FIG. 1 connects the main port 62 with the outlet 20. Of course, the position of the control shaft 50 may be changed so as to reverse the functions of the inlet 18 and the outlet 20.

The auxiliary port 64 is connected to an outlet plenum 68 by the passageway 70 and the auxiliary port 66 is connected to an inlet plenum 72 by the passageway 74. The plenum 72 is also connected to the main inlet port 60 through a restricted passageway 76 and the outlet plenum 4- 68 is connected to the main outlet port 62 through a re stricted passageway 78. It will be seen from FIGS. 3 and 4 that the restricted passageways 76 and 78 are notably smaller in flow cross-section than the ports 64, 74 and passages 70, 74. The cylindrical barrel body 32 rotates in a clockwise direction as indicated by the arrow with respect to the valve plate 22. As the barrel body 32 rotates the cylinder slots 36 sweep past the main ports 60 and 62 and the auxiliary ports 64 and 66 in succession.

The inlet plenum chamber 72 is kept at the inlet system pressure by the restricted connection 76 to the main inlet port 68 and the outlet plenum is maintained at the outlet system pressure by the restricted connection 78. The two plenum chambers 68 and 72 provides fluid to pressurize or depressurize each piston at the end of its travel, during a short period before it is exposed to the valve port. This is accomplished through the auxiliary ports 64 and 66. As the cylinder slot 36 moves with the barrel body 32 toward the main inlet port 68 a portion of the cylinder slot 36 sweeps across the auxiliary port 66 so as to provide a connection for the fluid in the plenum chamber 72 to the inside of the cylinder 34 through the passageway 74. This fluid pressurizes or depressurizes the cylinder 36 so that it will have approximately the same pressure as the inlet system whatever small fluid pulse occurs in the inlet plenum chamber 72 by sudden equalization of pressure between that chamber and the cylinder 34 is severely damped by the restrictive passageway 76 in its transmission to the hydraulic system to which the pump is connected. When the cylinder slot 36 reaches the main inlet port 60, the piston 42 draws fluid through the inlet system. The pressures of the cylinder 34 and the inlet system are approximately equal at this time due to the connection of the cylinder with the plenum chamber. Similarly when the cylinder slot 36 approaches the main outlet port 62 a portion of the cylinder slot first sweeps across the auxiliary port 64 so as to introduce fluid from the plenum chamber 68 into the cylinder 34. This equalizes the pressure in the cylinder 34 and the pressure in the outlet system. Of course, whatever small pulse or shock occurs in the outlet plenum chamber 68 by sudden equalization of pressure between that chamber and the cylinder 34 is severely damped by the restrictive passageway 78 in its transmission to the hydraulic system to which the pump is connected. In this way noise from unequal pressure is reduced during the upward stroke and the downward stroke of the piston 42.

It can be seen that this pressure equalizing mechanism will operate whether the pump is pumping or overhauling and whether it is pumping or overhauling from right to left or from left to right. In any case the cylinder slots 36 will come into contact with a plenum chamber prior to coming into contact with one of the main ports. The plenum chamber will remain at the same pressure as its corresponding port.

A longitudinal cross-sectional view of the valve plate 22 is shown in FIG. 4, having a cylindrical shaft 24 rotatively passing through its center and three metal plates 82, 84 and 86 placed side by side so as to form the valve plate itself. Each of the adjacent cylindrical plates 82, 84 and 86 have two circular slots cut in them at corresponding locations so as to form the main ports 66 and 62, which pass through the valve plate 22. These main ports provide a connection between the cylinders 34 and the passageways 38 and 40 which lead to the inlet 18 and the outlet 20 respectively. The cylindrical plate 84 which is placed in between the plate 82 and the plate 86 has two additional circular slots cut into it further out radially than the slots which form the main ports 60 and 62. These slots form the two plenum chambers 72 and 68 when covered on one side by the plate 82 and on the other side by the plate 86. The restricted passageways 76 and '78 are also cut in the plate 84 so as to form a connection between the plenum chambers and the main ports. The auxiliary port 64 is also cut in the top plate 82 so as to form a connection with the passageway '70 which is cut in the center plate 84 and which is in communication with the outlet plenum 68. The three plates 82, 84 and 86 may be brazed together. The plate could also be made of a single piece using straight drilled holes for chambers and for chamber openings.

A fragmentary cross-sectional view of the valve plate and the barrel assembly during a cylinder pressurizing stage is shown in FIG. 5 having a piston 42 located in the cylinder 34. The barrel body 32 has been rotated such that the cylinder slot 36 is passing over the auxiliary port 64 which is cut in the plate 82 of the valve plate 22. The auxiliary port 64 is connected to the plenum chamber as which is cut in the plate 84 and bounded on the bottom by the plate 86 and on the top by the plate 82.

The fluid in the plenum chamber 68 is at the same pressure as the fluid in the main output port 62. Fluid will now flow between the cylinder 34 and the plenum chamber 63 so as to equalize the pressure and bring the cylinder 34 to approximately the same pressure as the output system of the pump. The barrel body 32 will now sweep across the 'main output port 62. Since the pressure in the cylinder 34 is approximately equal to the pressure of the output of the system there will be little noise caused by shock when the cylinder comes into contact with the output port 62.

If the swash plate 48 is mounted to rotate about a line normal to the axis of one of the pistons, rather than normal to the axis of the center line of the shaft, the pump itself may be used only for unidirectional flow. As pointed out above this arrangement has the advantages of allowing greater variation in the length of the stroke in the pistons, and also of keeping a minimum the volume in in each cylinder at zero stroke. However, this type of mounting of the swash plate only allows for pumping and overhauling in one direction. To obtain bi-directional flow a reversing valve assembly such as that shown in FIG. 6 must be used.

The flow reversing valve assembly shown in FIG. 6 comprises a shuttle valve means $3 and cam means o. The valve means 88 includes a valve body 92 and a three piston member 94 slidable within said valve body. A conduit 96 connects the valve means to the inlet passage 18 and conduit 98 connects the valve means to the outlet passage 20. A pair of conduits 1% and 102 connect the valve means with the load. Conduit 102 has a branch line 104 connected therewith so there are actually two connections to the valve body 92. The conduits 96, 98 and It?!) have enlarged orifices in the valve body 92 so that when the valve member 94 is in its natural or its center position (condition, as will be presently described, when the swash plate is vertical), crossflow can occur between the inlet 1d and the outlet 26.

A control rod 1% extends between the valve member 94 and the cam means 9%? for the purpose of controlling movement of said valve member. The cam means 9% includes a lower portion for controlling movement of the valve member 94 and an upper portion for controlling movement of the swash plate 48. The lower portion has a higher surface 1% and a lower surface lltl.

FIG. 6 shows the control rod 1% upon the higher surface, thus causing the valve member 9 to be moved to the left position. In this position, fluid flows into the the pump through the conduits 1G2 and 96 and out of the pump through the conduits 9S and 1%. If the cam means were shifted so that the control rod 106 bore upon the lower surface Ht), flow in the system would be reversed, since the valve member 94 would move to the right thus causing fluid to flow into the pump through the conduits ran and as and out of the pump through the conduits 98 and W2 (by means of the branch lines 1%).

The upper portion of the cam means 90 consists of two slope planar surfaces 112 and 114 which meet at a point 116. A control rod 118 rides along the surfaces 112 and 114 and has its other end linked to the control shaft 50 of the swash plate 48. Thus, it. can be seen that as the cam means 90 moves, the inclination of the swash plate is changed from full stroke inclination (at the highest portion of surfaces 112 and 114) to no inclination (at point Illa). When the control rod 118 is at the point 116, the control rod 106 is midway between surfaces 103 and 110, thus causing the valve member 94 to resume the neutral position previously referred to.

It can be seen that the pump of this invention combines the high etficiency, and low cost of manufacture of reciprocating pumps with a very low noise characteristic. The valve plate which is part of this pump may be substituted into other reciprocating pumps so as to incorporate many of the benefits of this invention. The pump of this invention may pump or overhaul either from left to right or right to left.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A pump comprising:

a rotor;

a plurality of cylinders located in a circle in said rotor and having axes parallel to and equidistant from the axis of rotation of said rotor;

a plurality of pistons located one to each of said cylinders;

inlet means for passing fluid into said pump;

outlet means for passing fluid out of said pump;

inlet-reservoir means for confining fluid at the pressure of said inlet means, said inlet reservoir means communicating through a first restricted passageway with said inlet means, and said first restricted passageway being continuously open to fluid flow in both directions;

outlet-reservoir means for confining fluid at the pres sure of said outlet means, said outlet reservoir means communicating through a second restricted passageway with said outlet means, and said second passageway being continuously open to fluid flow in both directions;

cam means for reciprocating said plurality of pistons within said plurality of cylinders as said rotor rotates so as to transfer fluid in and out of said plurality of cylinders; and

valve means for passing said fluid which is transferred out of said cylinders to said outlet means, for passing said fluid which is transferred into said cylinders from said inlet means, for connecting said inletreservoir means to said cylinders for a period of time after they have been connected to said outlet flians and before they are connected to said inlet means, and for connecting said outlet-reservoir means to said cylinders for a period of time after they have been connected to said inlet means and before they are connected to said outlet means.

2. A pump as defined in claim l, in which said inletreservoir means and said outlet-reservoir means are located within said valve means.

3. A pump as defined in claim 2, in which said valve means is a stationary disc having a first port adjacent to said inlet means for passing fluid into said cylinders from said inlet means, a second port adjacent to said outlet means for passing fluid into said outlet means from said cylinders, 21 third port located after said first port and before said second port in the path of said cylinders for connecting said cylinders to said outlet-reservoir means, and a fourth port located after said second port and before said first port in the path of said cylinders for connecting said cylinders to said inlet-reservoir means.

4. A variable-stroke parallelpiston hydraulic pump comprising:

a housing;

an inlet means;

an outlet means;

a shaft journaled in said housing and adapted to rotate;

a cylindrical barrel fixed upon said shaft and adapted to rotate therewith;

a plurality of cylinders located in said cylindrical barrel and arranged around and parallel to said shaft;

a plurality of pistons located one to each of said cylinders;

a condiut leading from each cylinder to the back of said cylindrical barrel;

a bearing arranged around said cylindrical barrel to rotatably support said cylindrical barrel Within said housing;

a plurality of piston rods one for each of said plurality of pistons;

said piston rods extending beyond the front end of said cylindrical barrel and having a bearing on the far end;

motor means for rotating said cylindrical barrel;

cam means fixed to said housing and movably contacting said piston-rod bearings for reciprocating said plurality of pistons as said cylindrical barrel rotates so as to transfer fluid in and out of said plurality of cylinders;

inlet-reservoir means, connected through a first restricted passageway to said inlet means, or confining fluid at the pressure of said inlet means, said first restricted passageway being continuously open to fiuid fiow in both directions;

outlet-reservoir means, connected through a second restricted passageway to said outlet means, for confining fluid at the pressure of said outlet means, said second restricted passageway being continuously open to fluid flow in both directions; and

cylindrical valve means adjacent to the back end of said cylindrical barrel and fixed to said housing;

said cylindrical valve means having a first port adjacent to said inlet means for passing fluid into said cylinders from said inlet means, a second port adjacent to said outlet means for passing fiuid into said outlet means from said cylinders, a third port located after said first port and before said second port in the path of said cylinders for connecting said cylinders to said outlet-reservoir means, and a fourth port located after said second port and before said first port in the path of said cylinders for connecting said cylinder to said inlet-reservoir means.

5. Valve structure for a parallel piston hydraulic pump,

said valve structure comprising:

a piate member presenting a surface adapted to close the cylinders of a hydraulic pump during relative movement between said cylinders and said plate member;

said plate member having a first port to enable fluid to flow between the inlet of said hydraulic pump and said cylinders, said plate member having a secend port to enable fluid to flow between said cylinders and the outlet of said hydraulic pump;

means defining a reservoir chamber communicating with one of said first and said second ports through a restricted passageway which is continuously open to fluid flow in both directions; and

said plate member having an auxiliary port communicating with said chamber independently of said restricted passageway, said auxiliary port being located so that each of said cylinders traverses said auxiliary port before traversing said one of said first and second ports with which said reservoir chamber communicates through said restricted passageway.

6. Valve structure for a parallel-piston hydraulic pump, said valve structure comprising;

a plate member presenting a surface adapted to close the cylinders of a pump when said cylinders are supported for relative movement along a predetermined path with respect to said plate member;

said plate member having a main inlet port and a main outlet port in said surface so as to sequentially communicate with said cylinders during said relative movement;

means defining a first reservoir chamber communicating through a first restrictive passageway with said main inlet port, and means defining a second reservoir chamber communicating through a second restrictive passage way with said main outlet port, said first and second restricted passageways being continuously open to fluid flow in both directions;

said plate member further having a first auxiliary port communicating with said first reservoir chamber independently of said first restricted passage, and a second auxiliary port communicating with said second reservoir chamber independently of said second restricted passage, said first and second auxiliary ports being located in said path of travel prior to said main inlet and main outlet ports respectively; and

said restrictive passageways being smaller in section than said auxiliary ports whereby pulses occurring in said reservoir chambers upon equalization of pressures between said reservoir chambers and said cylinders through said auxiliary ports are damped by said restrictive passag ways in transmission to a hydraulic system to which the pump is connected.

7. A valve structure for a parallel-piston hydraulic pump as defined in claim 6, and wherein said means defining said first and second reservoir chambers comprises a portion of said plate member.

References Cited by the Examiner UNITED STATES PATENTS 2,237,018 4/41 Tweedale.

2,553,655 5/51 Herman et al. "103-162 2,619,041 11/52 Born 103162 2,661,695 12/53 Ferris 103--162 2,963,983 12/60 Wiggerman 103-122 LAURENCE V. EFNER, Primary Examiner. 

1. A PUMP COMPRISING: A ROTOR; A PLURALITY OF CYLINDRICAL LOCATED IN A CIRCLE IN SAID ROTOR AND HAVING AXES PARALLEL TO AND EQUIDISTANT FROM THE AXIS OF ROTATION OF SAID ROTOR; A PLURALITY OF PISTONS LOCATED ON TO EACH OF SAID CYLINDERS; INLET MEANS FOR PASSING FLUID INTO SAID PUMP; OUTLET MEANS FOR PASSING FLUID OUT OF SAID PUMP; INLET-RESERVOIR MEANS FOR CONFINING FLUID AT THE PRESSURE OF SAID INLET MEANS, SAID INLET RESERVOIR MEANS COMMUNIATION THROUGH A FIRST RESTRICTED PASSAGEWAY WITH SAID INLET MEANS, AND SAID FIRST RESTRICTED PASSAGEWAY BEING CONTINUOUSLY OPEN TO FLUID FLOW IN BOTH DIRECTIONS; OUTLET-RESERVOIR MEANS FOR CONFINING FLUID AT THE PRESSURE OF SAID OUTLET MEANS, SAID OUTLET RESERVOIR MEANS COMMUNICATING THROUGH A SECOND RESTRICTED PASSAGEWAY WITH SAID OUTLET MEANS, AND SAID SECOND PASSAGEWAY BEING CONTINUOUSLY OPEN TO FLUID FLOW IN BOTH DIRECTIONS; CAM MEANS FOR RECIPROCATING SAID PLURALITY OF PISTONS WITHIN SAID PLURALITY OF CYLINDERS AS SAID ROTOR ROTATES SO AS TO TRANSFER FLUID IN AND OUT OF SAID PLURALITY OF CYLINDERS; AND VALVE MEANS FOR PASSING SAID FLUID WHICH IS TRANSFERRED OUT OF SAID CYLINDERS TO SAID OUTLET MEANS, FOR PASSING SAID FLUID WHICH IS TRANSFERRED INTO SAID CYLINDERS FROM SAID INLET MEANS, FOR CONNECTING SAID INLETRESERVOIR MEANS TO SAID CYLINDERS FOR A PERIOD OF TIMER AFTER THEY HAVE BEEN CONNECTED TO SAID OUTLET MEANS AND BEFORE THEY ARE CONNECTED TO SAID INLET MEANS, AND FOR CONNECTING SID OUTLET-RESERVOIR MEANS TO SAID CYLINDERS FOR A PERIOD OF TIME AFTER THEY HAVE BEEN CONNECTED TO SAID INLET MEANS AND BEFORE THEY ARE CONNECTED TO SAID OUTLET MEANS. 